Liquid Water On Mars May Have Resulted From Hydrogen-Caused Greenhouse Effect

The combination of molecular hydrogen, carbon dioxide and water could have created a greenhouse effect on Mars nearly four billion years ago, raising temperatures to the point that liquid water could exist, according to research appearing in the latest edition of the journal Nature Geoscience.

That could help explain Nanedi Valles, which according to the study authors is a large valley on the Red Planet, comparable to the Grand Canyon, that suggests liquid water once flowed across the landscape. Previous efforts to produce temperatures warm enough to allow for the existence of liquid water on Mars used climate models that excluded molecular hydrogen, and those simulations proved unsuccessful.

However, Penn State University doctoral student Ramses M. Ramirez and his colleagues used a model which demonstrated that an atmosphere containing adequate amounts of CO2, H2O and molecular hydrogen could have allowed the planet’s surface temperature to rise above freezing. Those warmer temperatures would have allowed liquid water to flow, forming Nanedi Valles and other valleys.

“This is exciting because explaining how early Mars could have been warm and wet enough to form the ancient valleys had scientists scratching their heads for the past 30 years,” Ramirez explained in a statement Sunday. “We think we may have a credible solution to this great mystery.”

He and his colleagues note that there is an alternative theory: that the Martian valley network was formed after large meteorites crash landed on the planet, creating steam atmospheres that ultimately rained out. However, they add that this mechanism is incapable of producing the tremendous volume of water needed to carve the valleys.

“We think that there is no way to form the ancient valleys with any of the alternate cold early Mars models,” Ramirez said. “However, the problem with selling a warm early Mars is that nobody had been able to put forth a feasible mechanism in the past three decades. So, we hope that our results will get people to reconsider their positions.”

The study authors developed a one-dimensional climate simulation in order to illustrate that gas levels from volcanic activity might have created sufficient hydrogen and carbon dioxide to create a greenhouse effect, thus increasing temperatures enough to allow liquid water to exist. Once the model was finished, Ramirez ran it using new hydrogen absorption data, simulating the reduced sunlight present during the early days of Mars.

“It's kind of surprising to think that Mars could have been warm and wet because at the time the sun was much dimmer,” explained Ramirez. Based on evidence collected from Martian meteorites, scientists believe that the planet’s mantle appears to be more reduced than Earth’s. A reduced mantle outgases more hydrogen in relation to water, the researchers said, thus strengthening the hydrogen greenhouse effect.

“The hydrogen molecule is symmetric and appears to be quite boring by itself,” he added. “However, other background gases, such as carbon dioxide, can perturb it and get it to function as a powerful greenhouse gas at wavelengths where carbon dioxide and water don't absorb too strongly. So, hydrogen fills in the gaps left by the other two greenhouse gases.”

Image 2 (below): This is a split panel comparing a section of Arizona's Grand Canyon on left against a section of Mars' Nanedi Valles on right. Nanedi Valles is located in the Lunae Palus quadrangle of Mars. The northern part of the Nanedi Valles image shows a river once cut through it, similar to the one flowing through the Grand Canyon. Although this section of Nanedi Valles is nearly 2.5 km in width, other portions are at least twice as wide. Slight morphological differences between the two canyons are attributable to the great age differences between the regions and the correspondingly higher degree of erosion on Mars. Credit: Penn State